This nebula is about 4x wider than it is tall (2048x512), and is built so that it can revolve completely around the viewer in a continuous loop, such as when it's wrapped across the inside of a 3D sphere or box.
The problem is that right now, when wrapped the border glares at you, and it's quite hideous. Does anybody know how to make the left and right edges of this picture seamless? Is there a special technique I'm missing?

For a texture to fit on a sphere is only needs to be 2 times as wide as high. To solve the seam problem you can use the offset filter(filter - other - offset) and then paint it away, perhaps using the clone brush. Your layers should be collapsed for this to work, so that you don't move just individual layers around. Alternatively you can also do this on each layer of course, if you think it's worth the effort.